S21.452A ICD-10-CM Code: Open bite of left back wall of thorax with penetration into thoracic cavity, initial encounter

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for S21.452A in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on S21.452A itself; “inherited from” names the category or block whose note applies here.

7th Character Guide

"The appropriate 7th character is to be added to each code from category S21"

• A — initial encounter (this page’s code)
• D — subsequent encounter
• S — sequela

How the encounter character is assigned. “Initial encounter” means the patient is receiving active treatment for the condition — it is not limited to the first visit, and a different or new provider giving active treatment still assigns it. “Subsequent encounter” covers care during the healing or recovery phase after active treatment. “Sequela” is for complications or conditions that arise as a direct result of the original condition.

ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.a (paraphrased by MedCoder).

Variant codes in this family

S21.452A, S21.452D, S21.452S

Character meanings are CMS's official 7th-character extensions for this family, as carried in each variant code's official description; variant codes are registry rows. The explanation of how the encounter character is assigned is MedCoder editorial, distinct from the official content above it.

Coder workflow for S21.452A

MedCoder structured workflow — derived from this code’s own official record

Before you code S21.452A

1. A 7th character is required in this family. Confirm the documented encounter: initial (active treatment), subsequent (healing or recovery phase), or sequela. This page’s code carries “A”. “Initial” means active treatment, not the first visit (Guidelines I.C.19.a).

   See the 7th Character Guide · Guide: 7th characters: initial, subsequent, sequela →

2. Laterality is coded in this family. Confirm the side documented — right, left, or bilateral — and select the matching code (this page’s code: left). The unspecified-side code applies only when the record states no side. Laterality is assigned from the documented side; where a bilateral code exists and both sides are documented, it is used instead of two unilateral codes (Guidelines I.B.13).

   ReviewS21.451A · right, S21.459A · unspecified

   Guide: Laterality coding →

3. S21.452A’s title joins a condition with an associated condition or complication. Confirm each component is documented. Where the classification presumes the link through the “with” convention, only a provider statement that the conditions are unrelated defeats it. A combination code is assigned only when it fully identifies the documented conditions; a required second code for the stage, type or manifestation is still reported when the notes ask for it (Guidelines I.B.9, I.A.15).

   Guide: Combination codes →

4. Confirm the injury type, the anatomical site at the most specific level documented, laterality where the family codes it, and the encounter for the 7th character. Each injury is coded separately unless the classification provides a combination code, and a superficial injury is not coded when a more severe injury of the same site is documented. Injury chapter guidelines (Guidelines I.C.19.b, I.C.19.b.1).

   Guide: 7th characters: initial, subsequent, sequela →

5. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with S21.452A. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the documentation support a condition named in S21.452A’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewS20.47, S28.1

2. Is the side documented?
   Yes → Select the code for the documented side (or the bilateral code when both sides are documented and one exists).
   No → Use the unspecified-side code only when the record states no side; a query is the alternative.

   ReviewS21.451A · right, S21.459A · unspecified

3. Is the encounter phase documented — active treatment, healing or recovery, or a sequela?
   Yes → Assign the matching 7th character; the variant codes are in the 7th Character Guide.
   No → The code is invalid without its 7th character — query for the missing element.

Consider S21.452A. Then review the Code Also note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

Anatomical site

At the most specific level the record states; a site the classification separates cannot be assumed from a procedure or a measurement.

Laterality

Right, left or bilateral as documented; unspecified only when the record states no side (Guidelines I.B.13).

Encounter type

Active treatment, healing or recovery phase, or sequela — the basis of the 7th character (Guidelines I.C.19.a).

The associated condition or complication

Whether the associated condition the title names is documented; the “with” convention presumes some links, and a provider statement that the conditions are unrelated defeats it (Guidelines I.A.15).

Open or closed; displaced or nondisplaced

Defaults apply when the record is silent: closed, and displaced (Guidelines I.C.19.c).

External cause, place and activity

For the external cause codes reported with the injury or poisoning, where documented (Guidelines I.C.20.a).

Official instructions as workflow

• Excludes1 — check before selecting S21.452A(2 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with S21.452A: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareS20.47, S28.1

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of S21.452A(11 notes)

  Coding workflow: The conditions named in this note are not included in S21.452A. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareT17.5, T18.1, T17.8, T17.4, T63.4

  See the official tabular notes · Guidelines I.A.12.b

• Code Also — related condition(9 notes)

  Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

  ReviewS26, S27, S22.3, S22.4, S24.0, S24.1

  See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Don’t confuse S21.452A with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of S21.452A — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• S20.47— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of superficial bite of back wall of thorax moves the case to S20.47; the two are not reported together unless documented as unrelated.

  Full comparison: S21.452A vs S20.47 →

• S28.1— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of traumatic amputation (partial) of thorax moves the case to S28.1; the two are not reported together unless documented as unrelated.

  Full comparison: S21.452A vs S28.1 →

• S21.451A— Laterality relationship (Review)

  Same condition; these differ only in which side is documented.

  The same condition on the other side; the documented side decides, and a bilateral code, where one exists, replaces the pair when both sides are documented.

  What moves you there: A documented right side moves the case to S21.451A.

  Full comparison: S21.452A vs S21.451A →

• S21.459A— Laterality relationship (Review)

  Same condition; these differ only in which side is documented.

  The same condition on the other side; the documented side decides, and a bilateral code, where one exists, replaces the pair when both sides are documented.

  What moves you there: A record that states no side takes S21.459A; a documented side moves it back to a sided code.

  Full comparison: S21.452A vs S21.459A →

• S21.452D— Encounter relationship (Review)

  Same underlying diagnosis, different encounter phase.

  The same diagnosis at a different phase of care; one encounter takes one 7th character.

  What moves you there: Documentation of a subsequent encounter moves the case to S21.452D.

  Full comparison: S21.452A vs S21.452D →

• S21.452S— Encounter relationship (Review)

  Same underlying diagnosis, different encounter phase.

  The same diagnosis at a different phase of care; one encounter takes one 7th character.

  What moves you there: Documentation of a sequela moves the case to S21.452S.

  Full comparison: S21.452A vs S21.452S →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

1. A 7th character applies in this family. Confirm the documented encounter matches the character assigned. See the official 7th-character definitions and this code’s variants
2. Laterality is coded in this family. Confirm the documented side matches the code — the opposite-side siblings are in the relationships section. See the opposite-side sibling codes
3. 9 Code Also notes — a second code may apply; the guidelines leave its sequencing to the circumstances of the encounter. See the Code Also notes
4. 2 Excludes1 entries — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes
5. 11 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

• MCC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name S21.452A or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 6 Code Also instructions: S23.1 — Subluxation and dislocation of thoracic vertebra (via S21.-), S24 — Injury of nerves and spinal cord at thorax level (via S21.-), S25 — Injury of blood vessels of thorax (via S21.-), S26 — Injury of heart (via S21.-), S27 — Injury of other and unspecified intrathoracic organs (via S21.-), S29 — Other and unspecified injuries of thorax (via S21.-).

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: MCC — Major Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 93 clinically related codes on its CMS exclusion list. Does not count toward severity when the stay groups to DRGs 957-959 (Other O.R. Procedures for Multiple Significant Trauma); DRGs 963-965 (Other Multiple Significant Trauma).

Named in the grouper logic of 5 MS-DRGs: DRG 913 (MDC 21), DRG 914 (MDC 21), DRG 963 (MDC 24), DRG 964 (MDC 24), DRG 965 (MDC 24).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):INJ013 — Open wounds of trunk, initial encounter (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as MCC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

S21.421A — Laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.422A — Laceration with foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.429A — Laceration with foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.431A — Puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.432A — Puncture wound without foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.439A — Puncture wound without foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.441A — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.442A — Puncture wound with foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.449A — Puncture wound with foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.451A — Open bite of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.459A — Open bite of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.90XA — Unspecified open wound of unspecified part of thorax, initial encounter, S21.91XA — Laceration without foreign body of unspecified part of thorax, initial encounter, S21.92XA — Laceration with foreign body of unspecified part of thorax, initial encounter, S21.93XA — Puncture wound without foreign body of unspecified part of thorax, initial encounter, S21.94XA — Puncture wound with foreign body of unspecified part of thorax, initial encounter, S21.95XA — Open bite of unspecified part of thorax, initial encounter, S27.50XA — Unspecified injury of thoracic trachea, initial encounter, S27.51XA — Primary blast injury of thoracic trachea, initial encounter, S27.52XA — Contusion of thoracic trachea, initial encounter, +72 more

Same condition, opposite side

Same category and title, differing only in which side of the body is affected.

S21.451A — Open bite of right back wall of thorax with penetration into thoracic cavity, initial encounter (right)Compare S21.452A vs S21.451A →, S21.459A — Open bite of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter (unspecified)Compare S21.452A vs S21.459A →

Same injury, other encounter phase

Same injury, coded at a different phase of treatment via the 7th character.

S21.452D — Open bite of left back wall of thorax with penetration into thoracic cavity, subsequent encounterCompare S21.452A vs S21.452D →, S21.452S — Open bite of left back wall of thorax with penetration into thoracic cavity, sequelaCompare S21.452A vs S21.452S →

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Open wounds of trunk, initial encounter).

S21.421A — Laceration with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.422A — Laceration with foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.429A — Laceration with foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.431A — Puncture wound without foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.432A — Puncture wound without foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.439A — Puncture wound without foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.441A — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.442A — Puncture wound with foreign body of left back wall of thorax with penetration into thoracic cavity, initial encounter, S21.449A — Puncture wound with foreign body of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.451A — Open bite of right back wall of thorax with penetration into thoracic cavity, initial encounter, S21.459A — Open bite of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter, S21.90XA — Unspecified open wound of unspecified part of thorax, initial encounter, S21.91XA — Laceration without foreign body of unspecified part of thorax, initial encounter, S21.92XA — Laceration with foreign body of unspecified part of thorax, initial encounter, S21.93XA — Puncture wound without foreign body of unspecified part of thorax, initial encounter, S21.94XA — Puncture wound with foreign body of unspecified part of thorax, initial encounter, S21.95XA — Open bite of unspecified part of thorax, initial encounter, S29.021A — Laceration of muscle and tendon of front wall of thorax, initial encounter, S29.022A — Laceration of muscle and tendon of back wall of thorax, initial encounter, S29.029A — Laceration of muscle and tendon of unspecified wall of thorax, initial encounter, +267 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Bite”; these codes share that main term but sit in a different category of the Tabular List.

S11.85 — Open bite of other specified part of neck (neck, throat), S11.95 — Open bite of unspecified part of neck (neck), S20.16 — Insect bite (nonvenomous) of breast (breast, superficial NEC, insect), S20.17 — Other superficial bite of breast (breast, superficial NEC), S20.36 — Insect bite (nonvenomous) of front wall of thorax (thorax, thoracic, superficial NEC, insect, front), S20.37 — Other superficial bite of front wall of thorax (thorax, thoracic, superficial NEC, front), S20.46 — Insect bite (nonvenomous) of back wall of thorax (thorax, thoracic, superficial NEC, insect, back), S20.47 — Other superficial bite of back wall of thorax (thorax, thoracic, superficial NEC, back), S20.96 — Insect bite (nonvenomous) of unspecified parts of thorax (thorax, thoracic, superficial NEC, insect), S20.97 — Other superficial bite of unspecified parts of thorax (thorax, thoracic, superficial NEC), S30.860 — Insect bite (nonvenomous) of lower back and pelvis (pelvis, superficial NEC, insect), S30.861 — Insect bite (nonvenomous) of abdominal wall (abdomen, abdominal, wall, superficial NEC, insect), S30.862 — Insect bite (nonvenomous) of penis (penis, superficial NEC, insect), S30.863 — Insect bite (nonvenomous) of scrotum and testes (testis, superficial NEC, insect), S30.864 — Insect bite (nonvenomous) of vagina and vulva (vulva, superficial NEC, insect), S30.865 — Insect bite (nonvenomous) of unspecified external genital organs, male (genital organs, external, male, superficial NEC, insect), S30.866 — Insect bite (nonvenomous) of unspecified external genital organs, female (genital organs, external, female, superficial NEC, insect), S30.867 — Insect bite (nonvenomous) of anus (anus, superficial NEC, insect), S30.86A — Insect bite (nonvenomous) of flank (flank, superficial, insect), S30.870 — Other superficial bite of lower back and pelvis (pelvis, superficial NEC), +135 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Partial Thromboplastin Time (PTT) Test, Prothrombin Time Test and INR (PT/INR)

Contextual Map

Every relationship of S21.452A in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run S21.452A with these 6 related codes in Claim Check

Hierarchy

• S00-T88 — Chapter 19: Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) (S00-T88)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S20-S29 — Injuries to the thorax[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Referenced by Code Also instructions

• S23.1 — Subluxation and dislocation of thoracic vertebra[Code Also](via S21.-): “open wound of thorax (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• S24 — Injury of nerves and spinal cord at thorax level[Code Also](via S21.-): “open wound of thorax (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• S25 — Injury of blood vessels of thorax[Code Also](via S21.-): “any associated open wound (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• S26 — Injury of heart[Code Also](via S21.-): “open wound of thorax (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• S27 — Injury of other and unspecified intrathoracic organs[Code Also](via S21.-): “any associated open wound of thorax (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026
• S29 — Other and unspecified injuries of thorax[Code Also](via S21.-): “any associated open wound (S21.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• INJ013 — Open wounds of trunk, initial encounter[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• MCC — Major Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (MCC). Not counted when the stay groups to DRGs 957-959 (Other O.R. Procedures for Multiple Significant Trauma); DRGs 963-965 (Other Multiple Significant Trauma).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 913 — TRAUMATIC INJURY WITH MCC[MS-DRG]: “TRAUMATIC INJURY WITH MCC (MDC 21)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 914 — TRAUMATIC INJURY WITHOUT MCC[MS-DRG]: “TRAUMATIC INJURY WITHOUT MCC (MDC 21)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 963 — OTHER MULTIPLE SIGNIFICANT TRAUMA WITH MCC[MS-DRG]: “OTHER MULTIPLE SIGNIFICANT TRAUMA WITH MCC (MDC 24)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 964 — OTHER MULTIPLE SIGNIFICANT TRAUMA WITH CC[MS-DRG]: “OTHER MULTIPLE SIGNIFICANT TRAUMA WITH CC (MDC 24)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 965 — OTHER MULTIPLE SIGNIFICANT TRAUMA WITHOUT CC/MCC[MS-DRG]: “OTHER MULTIPLE SIGNIFICANT TRAUMA WITHOUT CC/MCC (MDC 24)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 21 — Injuries, Poisonings and Toxic Effects of Drugs[MDC crossing]: “Injuries, Poisonings and Toxic Effects of Drugs — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 32,029 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026
• MDC 24 — Multiple Significant Trauma[MDC crossing]: “Multiple Significant Trauma — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 22,957 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Nearest codes (40)

• S21 — Open wound of thorax[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.439S — Puncture wound without foreign body of unspecified back wall of thorax with penetration into thoracic cavity, sequela[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.44 — Puncture wound with foreign body of back wall of thorax with penetration into thoracic cavity[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.441 — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.441A — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, initial encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.441D — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, subsequent encounter[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.441S — Puncture wound with foreign body of right back wall of thorax with penetration into thoracic cavity, sequela[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• S21.442 — Puncture wound with foreign body of left back wall of thorax with penetration into thoracic cavity[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 32 more

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to S21.452A in its code family, with their registry titles.

• S21.451 — Open bite of right back wall of thorax with penetration into thoracic cavity
• S21.451A — Open bite of right back wall of thorax with penetration into thoracic cavity, initial encounter
• S21.451D — Open bite of right back wall of thorax with penetration into thoracic cavity, subsequent encounter
• S21.451S — Open bite of right back wall of thorax with penetration into thoracic cavity, sequela
• S21.452 — Open bite of left back wall of thorax with penetration into thoracic cavity
• S21.452D — Open bite of left back wall of thorax with penetration into thoracic cavity, subsequent encounter
• S21.452S — Open bite of left back wall of thorax with penetration into thoracic cavity, sequela
• S21.459 — Open bite of unspecified back wall of thorax with penetration into thoracic cavity
• S21.459A — Open bite of unspecified back wall of thorax with penetration into thoracic cavity, initial encounter
• S21.459D — Open bite of unspecified back wall of thorax with penetration into thoracic cavity, subsequent encounter

View all codes in the S21 family